The use of scanning technology and reverse engineering software has enabled one designer to build a gearbox that would not only fit within a classic car’s engine bay but would align correctly with other components
In his spare time, Brian Coombs, engineering lead for mechanical design at Bloodhound SSC, is upgrading the engineering of, and rebuilding, a replica of the classic Ford GT40 sports car. The car has a five-litre V8 engine, but the car kit he bought a few years back couldn’t handle this, and the gearbox tended to fail under the power.
Coombs therefore decided to build his own gearbox using the internal parts from an old Reynard Indy racing car. He had the skills required for this due to his background in design engineering in the motor-sport industry – as well as leading the engineers that were responsible for the mechanical structure and suspension system for the Bloodhound, he has worked for the Red Bull Racing Formula 1 team amongst other motor racing teams. He is also used to working with today’s CAD/CAM technologies.
So, rather than using only traditional manual methods to rebuild his car, Coombs has set up his own machine shop and has access to 3D CAD, in the form of Siemens NX software, to redesign certain parts of the car and to create a 3D digital CAD model of it, from which new parts could be manufactured.
The gearbox, however, presented a challenge. As he would be making the gearbox out of existing components, he needed to be sure that, once complete within a suitable casing, it would fit into the available space in the car’s engine bay, that it wouldn’t foul other parts of the car and that it would align correctly with other components. While there was the option of manually placing this and taking the measurements, this would have been very time-consuming.
It turned out, however, that by using a Rexcan 3D scanner from Solutionix, it would be possible to scan the gearbox casing and then use Geomagic Studio 3D imaging and reverse engineering software to create an accurate 3D digital model of it from the scan data. This model could then be used for ‘volume claim’ packaging purposes in Coombs’ CAD system.
A Rexcan 420 from the company’s Rexcan structured light 3D scanners was used to capture the shape of the gearbox casing. With its twin CCD cameras with resolutions up to eight mega-pixels and using phase-shifting optical triangulation technology, the Rexcan 4 is capable of capturing millions of 3D coordinate points per second to an accuracy of ±20 microns.
The scanner was used in conjunction with a Solutionix automatic turntable that can handle items weighing up to 70kg. With the gearbox casing mounted on the turntable, the scanner was set up to look down on it at 45°. With Solutionix ezScan software controlling and coordinating the turntable’s motion and the scanner’s data capture processes, scans of the upper half of the casing were taken automatically at increments of 10° as the turntable rotated through 360°. The casing was then turned over and the process was repeated in order to capture the lower half.
A total of 72 individual scans were taken in a session lasting around an hour. With the ezScan software, the individual scans were registered with each other automatically as the scanning was proceeding to create a single 3D point cloud model of the gearbox casing. This was then converted by the scanning software into a single, merged polygon model.
Although comprising only about a fifth of the total number of polygons contained in all the individual scans, the merged scan data model still comprised some 10 million polygons. So to speed up subsequent processing of the data, the model was sampled, reducing the polygon count in flat areas while retaining it in high curvature areas. This reduced the polygon count to around one million without affecting the model’s accuracy.
3D surface model
Next in the process was converting the polygon model into an accurate 3D digital surface model suitable for use in the CAD system. For this it was exported from the Solutionix scanning system into Geomagic Studio 3D imaging and reverse engineering software.
The first step was to repair the polygon model where required, using Geomagic Studio’s standard tools to fill holes in the model where the scanning process had not succeeded in fully capturing certain parts of the casing. In just ten minutes, this process resulted in a single, fully closed – or ‘water-tight’ – 3D polygonal model.
The software’s ‘Create Features’ function was then used to select and identify simple geometric features, such as cylinders, holes and planes on the model that would be used to provide a geometric reference within the CAD system. Finally, the software’s AutoSurface command was used to convert the polygon model, incorporating the geometric features, into a NURBS (non-uniform rational b-spline) surface model. This was a two-clicks automatic process that took around two minutes to calculate. A straightforward ‘3D Compare’ between the polygon model and the surface model was then used to confirm the geometric integrity of the final surface model.
Once this was all done, the final model was ready to be exported to Coombs’ CAD system as a STEP (.stp) file where it could be used as a volume claim model within the 3D CAD model of the car’s chassis, sub-frame and suspension system. This would ensure that, when it came to physically installing the new gearbox, it would fit into its space and align correctly with other parts.
Scanning the gearbox casing and creating an accurate 3D digital surface model of it took around two hours.
Coombs commented: “The near-automatic scanning process using the Solutionix scanner and turntable, along with the automatic processing of the scan data provided by the Solutionix ezScan and Geomagic Studio 3D imaging and reverse engineering software – most of which is accomplished with just one or two mouse clicks – saved a lot of time.”
Despite the speed in which this was carried out, Coombs was impressed with the resolution and accuracy of the original scan data, as well as the quality of the final 3D digital surface model and the way this could easily be incorporated into the CAD model.
He added: “This meant I could be confident that what I was doing in the virtual world would work in the real world on the car.”
Once complete, Coombs plans to enter the Ford GT40 replica in the occasional race.